Segmented polyurethanes are used in the manufacture of many conventional blood-contacting medical devices, such as pacemaker leads and connectors, vascular grafts, self-sealing arteriovenous access grafts and diagnostic catheters (1-3). The chemical structure of such polyurethane elastomers provides high tensile strength, lubricity, good abrasion resistance, ease of handling, such as extruding and bonding, and good "biocompatibility" (3,4). Although the devices provide useful short-term utility, their long-term function still remains a problem (5). One deficiency of these devices is due to the foreign nature of the implant materials with respect to the body and leads to the eventual degradation of the material (6). The consequences of the material degradation of the device inside the body includes the loss of materials' tensile strength and surface cracking (7,8). It has been found that hydrolysis and oxidation of polyurethanes in vivo were both possible causes of the degradation (8,9). In addition to the degradation of the polyurethanes, thrombus formation on the surface of polyurethane materials also presents a problem. Attempts to overcome the thrombus problem include the incorporation of heparin (10), albumin (11) and endothelial cells (12). The permanent binding of biologically active moieties to polymer chains or polymer surfaces has also been studied (13, 14). However, the main drawback of these biologically modified materials is that they suffer from the lower reproducibility of the surface modification and the effective lifetime of the components. Thus, although some new polymers have been developed with improved stability (7), no satisfactory alteration of polyurethanes has been attained.
The addition of polymeric surface additives into base polyurethanes in order to change the surface chemistry while the bulk properties are kept intact has been studied (15).
U.S. Pat. No. 4,861,830--Ward et al, issued Aug. 29, 1989, describes polymer admixtures formed from a base polymer and thermoplastic copolymer additives having polar hard segments and polar and non-polar soft blocks in graft or block copolymer form, for use in biomedical devices. U.S. Pat. No. 5,235,003--Ward et al, issued Aug. 10, 1993, describes novel linear polysiloxane-polyacetone block copolymers, particularly polysiloxane-polycaprolactone linear blocked copolymers, miscible with nylon for use as surface-modified nylon articles. U.S. Pat. No. 4,935,480--Zdrahala et al, issued Jun. 19, 1990, describes non-blocking hemocompatible, thermoplastic, fluorinated polyetherurethanes made from polyether glycols, isocyanates, chain extenders and non-fluorinated polyols. The method of preparation includes two steps in which the fluorinated glycol is reacted initially with the diisocyanate to give a prepolymer having terminal isocyanate groups. The prepolymer is subsequently reacted with the chain extender and non-fluorinated polyol. The fluorinated polyetherurethane has use in medical devices.
Ward et al (16) describes the presence of surface-active oligomeric terminal groups in linear base polymer polyurethaneureas as new biomaterials. Y. -W. Tang et al (17) describes a series of fluorine-containing polyurethane surface-modifying macromolecules having improved bioresistance and biocompatibility.
Fluorinated polymers are generally hydrolytically stable materials and have been used as coating materials (18). In addition, fluorinated polymers have exhibited good blood compatibility characteristics. The graft of a perfluorodecanoic acid to a polyurethane has been shown to enhance blood compatibility (19). This study focused on the use of modifying techniques for polyurethanes that contain fluoropolymeric segments. The macromolecular additives were introduced into the base polyurethane with the purpose of altering the surface chemistry without compromising the bulk properties of the base polyurethane.
However, there is, still, a need for materials for use in the manufacture of articles having acceptable surface properties, particularly, medical device implants requiring improved mechanical properties, blood compatibility and long term biostability.